Between the Covers — Kira Stone

Petite and plump, Leah Spencer has a perfectly ordinary and boring life as a librarian at the local college, until she encounters people, lots of people, using a certain section of the library as a trysting place. There's something in the book stacks that makes everyone into raving nymphomaniacs, and with the help of Samuel Zheng, the college's Head of Security, she's got to figure out what it is and put a stop to it.

The upside to all of this is that plain, plus-sized Leah has been “touched” by whatever force is creating all of this desire, and she and Sam get to know each other quite intimately as this tale progresses. In their quest to get to the bottom of all of this, they encounter a host of fascinating and otherworldly creatures, and come to take their places in the battle between good and evil.